Cooling of buildings consumes a huge amount of energy worldwide. For example, in the Sunbelt States of the US, including Alabama, Arizona, California, Florida, Georgia, Louisiana, Mississippi, Nevada, New Mexico, South Carolina, and Texas, air conditioning is the dominant end user of energy and the single leading cause of peak demand for electricity. From an economics point of view, reducing electricity demand for space cooling could save a lot for consumers. From a utility-infrastructure point of view, reducing air-conditioning electricity loads can lower demand for annual power generation and peak capacity. Coincidentally, in regions where air conditioning is needed the most, solar energy is also abundant. Especially, from day to day, the stronger the sunlight, the more air conditioning power is needed. Therefore, to utilize sunlight to power air conditioning is a logical solution.
Air conditioners using solar energy have been disclosed, for example, in U.S. Pat. Nos. 5,375,429, 5,878,584, 6,539,738, and 6,880,553. There is a common drawback of those methods: Solar energy is only available in sunny days, not in evenings and nights. By directly using the solar electricity to drive an air-conditioning unit to cool the rooms, it does not provide a relatively constant temperature throughout the entire day and night. Right after sunset, when the environment is still very hot, the solar power disappears. And the maximum cooling effect from direct sunlight is at noon time, which is not the hottest time of the day (the hottest time in a day is about 3-5 pm). In the evenings and nights, although air conditioning is still needed, there is no sunlight. Sunlight is also absent in cloudy and raining hours.
To resolve this problem, methods to store cooling power using ice have been disclosed in the 1980s, with the purpose of taking advantage of the price difference of electricity in peak time and night, mostly for large commercial buildings. On the other hand, for the cooling of vehicles and boats, the use of ice as a storage method for cold energy was disclosed in U.S. Pat. Nos. 5,237,832 and 7,062,923. The problem with those approaches is that when water is frozen to ice, the volume increases by 9%, and the expanding ice could damage the container and the heat-exchange coils. For air conditioners in buildings, the amount of ice is a good fraction of one ton or more than one ton, and the potential damage to the containers and tubes can be significant.
During the research for patent application Ser. No. 12/135,113, it is found experimentally that by freezing a mixture of 10% of glycerin, 5% of alcohol and 85% water, thin sheets of ice are formed, and the specific gravity of the ice sheets are similar to that of the liquid. In other words, with a proper composition, there is no significant expansion during freezing. As a result, the ice sheets do not stay at the top of the container. Instead, the ice sheets disperse over the entire volume. Mechanically, those thin sheets of ice are fragile and mobile, which will not damage the container as well as the tubes. Therefore, such mixtures are suitable to use as cold energy storage for air conditioners.
The present invention is related to a design of a solar-powered air conditioning system which utilizes the DC current directly from the solar cells to drive a vapor-compression refrigeration unit to freeze a mixture of glycerin, alcohol and water (typically 5%-10% of glycerol, 2.5% to 5% of alcohol, and 85%-90% of water), then use the stored cooling power of the partially frozen glycerin-alcohol-water mixture to cool the building. Because the low cost of crude glycerin and industry-grade alcohol, the elimination of the inverter and power distribution facilities, and the simplicity of the apparatus, the solar-powered air conditioning system could have a significant impact on energy savings.